“Teacher Star, I often wonder, how do all the delicious foods we eat turn into energy for our bodies?” Leona asked curiously, holding a thick biology textbook.

Teacher Star smiled mysteriously and said, “It’s not just about the 'pipes' of the digestive tract! Our bodies hide a super powerful 'Chemical Breakdown Squad,' which are the digestive glands. They secrete digestive fluids to help!”

Teacher Star continued, “First, there are the 'salivary glands.' When you take a big bite of rice, they start secreting saliva in your mouth, initiating the breakdown of carbohydrates, turning large molecules into smaller ones, making food easier to swallow.”

“Then the food enters the stomach, and it's the 'gastric glands'' turn! The gastric juice they secrete is specialized for proteins, cutting protein molecules like scissors, preparing them for further digestion.”

Leona touched her stomach, suddenly enlightened, “So the stomach doesn't just churn, it also has chemical reactions!” Teacher Star nodded, “Exactly! Next, our 'liver' also helps. It secretes bile, which doesn't directly break down fats but emulsifies them, turning large fat clumps into tiny oil droplets, making them easier to break down later.”

“The most amazing superhero is the 'pancreas'!” Teacher Star said mysteriously, “The pancreatic juice it secretes is incredibly versatile, capable of breaking down carbohydrates, proteins, and lipids – all three major nutrients. It's the multi-talented master of digestive fluids!”

“Finally, there are the 'intestinal glands,' which secrete intestinal juice, responsible for completing the final breakdown to ensure all nutrients are small enough.” Leona listened intently, “Wow, so many different digestive fluids, why can't one type handle everything?”

Teacher Star smiled and explained, “It's like locks and keys; each nutrient has a different structure and requires a specific digestive fluid to 'unlock' it. For instance, starch needs the combined effort of salivary, pancreatic, and intestinal juices to be broken down into glucose.”

“Proteins are similar; they need the team of gastric, pancreatic, and intestinal juices to be finally broken down into amino acids. Lipids are even more special: they must first be emulsified by bile into tiny oil droplets, and then pancreatic juice takes over to break them down into fatty acids and glycerol.”

“Once all these nutrients become small molecules, they are ready to enter our 'small intestine'!” Teacher Star pointed to a diagram of the human digestive system. “The inner wall of the small intestine is covered with countless brush-like villi, greatly increasing the absorption area, delivering nutrients throughout the body. Without the prior efforts of the digestive glands, the small intestine wouldn't be able to absorb anything!”